Methods and systems for fluid control in microfluidic devices

Abstract

The present invention relates to a valve for use in a microfluidic system. The valve includes a substrate defining an upstream channel and a downstream channel joined by a passage, wherein the passage comprises a first opposed wall disposed at an angle to a central axis of the upstream channel. A thermally responsive substance (TRS) obstructs the passage. At least a portion of the TRS that obstructs the passage abuts the first opposed wall. Upon the actuation of the heat source in thermal contact with the TRS an opening motion of the TRS opens the passage.

What is claimed is:  
     
       1. A valve for use in a microfluidic system, comprising: 
       a substrate defining an upstream channel and a downstream channel joined by a passage, the passage comprising a first surface; and  
       a thermally responsive substance (TRS) disposed, when the valve is in the closed state, to substantially obstruct the passage, wherein pressure present in the upstream channel urges at least a portion of the TRS against the first surface; and  
       a reservoir adjacent the passage, wherein, upon an opening motion of the TRS, at least at least a portion of the TRS moves into the reservoir thereby opening the passage.  
     
     
       2. The valve of  claim 1 , wherein the passage defines a central axis and the first surface is disposed at an angle to the central axis. 
     
     
       3. The valve of  claim 1 , further comprising a microfabricated heat source in thermal contact with the TRS. 
     
     
       4. The valve of  claim 1 , wherein the substrate is a planar substrate and the upstream channel, downstream channel, and passage are etched in a surface of the substrate. 
     
     
       5. The valve of  claim 1 , wherein the passage further comprises a second surface disposed at a second angle to the central axis, and wherein at least a second portion of the TRS that obstructs the passage abuts the second surface. 
     
     
       6. The valve of  claim 5 , wherein the first and second surfaces protrude into the passage. 
     
     
       7. The valve of  claim 5 , wherein the first and second surfaces form a restriction therebetween. 
     
     
       8. The valve of  claim 1 , wherein the substrate comprises silicon. 
     
     
       9. The valve of  claim 3 , further comprising a second, different substrate and wherein the microfabricated heat source is microfabricated on a surface of the second, different substrate. 
     
     
       10. The microfluidic system of  claim 3 , wherein the heat source comprises a heating element disposed at a second surface of the second substrate, the second surface of the second substrate being opposite the first surface of the second substrate. 
     
     
       11. A method for producing a valve for a microfluidic system, comprising: 
       providing a first substrate having a first planar surface and a second, different substrate having a first planar surface, a portion of the first planar surface of the first substrate bonded with a portion of the first planar surface of the second substrate, whereby the first and second substrates define, therebetween, a passage that joins an upstream channel and a downstream channel of the microfluidic system, the passage comprising a retaining surface; and  
       introducing a mass of temperature responsive material (TRS) into the passage, wherein introducing the mass of TRS comprises heating the passage to allow motion of the TRS therein, and wherein, when the valve is in the closed state, pressure in the upstream channel urges the TRS against the retaining surface.  
     
     
       12. A method for producing a valve for a microfluidic system, the valve being produced in the closed state, comprising: 
       providing a substrate defining a passage that joins an upstream and a downstream channel of the microfluidic system; and  
       introducing a mass of temperature responsive material (TRS) into a reservoir channel adjacent the passage, wherein capillary action draws the TRS into the passage, and wherein, upon being drawn into the passage, the TRS obstructs the passage and a surface tension of the TRS substantially prevents the TRS in the passage from entering the upstream or downstream channel.  
     
     
       13. A microfluidic system comprising a valve for providing a passage between an upstream and a downstream channel of the microfluidic system, the [valve] microfluidic system comprising: 
       a first substrate having a first planar surface and a second, different substrate having a first planar surface, a portion of the first planar surface of the first substrate bonded to a portion of the first planar surface of the second substrate, whereby the first and second substrates define, therebetween, at least an upstream channel and a downstream channel joined by a passage; and  
       a temperature responsive substance (TRS), wherein, at a first temperature, the TRS is disposed to obstruct the passage, and wherein, at a second temperature, at least a portion of the (TRS) enters the downstream channel, thereby opening the passage.  
     
     
       14. The valve of  claim 13 , wherein at least about 75% of the TRS that obstructs the passage enters the downstream channel upon the opening of the passage. 
     
     
       15. A microfluidic system comprising a valve for providing a passage between upstream and downstream channels of the microfluidic system, comprising: 
       a first substrate having a first planar surface and a second, different substrate having a first planar surface, a portion of the first planar surface of the first substrate bonded to a portion of the first planar surface of the second substrate, whereby the first and second substrates define, therebetween, at least an upstream channel and a downstream channel joined by a passage;  
       a temperature responsive substance (TRS) configured to substantially obstruct the passage;  
       a heat source disposed in thermal contact with the (TRS), wherein, upon actuation of the heat source, at least a portion of the (TRS) enters the downstream channel, thereby opening the passage.  
     
     
       16. The valve of  claim 15 , wherein the passage comprises a first surface, wherein pressure present in the upstream channel urges at least a portion of the TRS against the first surface. 
     
     
       17. The valve of  claim 16 , wherein the passage further comprises a second surface, wherein pressure present in the upstream channel urges at least a portion of the TRS against the second surface. 
     
     
       18. The valve of  claim 17 , wherein the first and second opposed walls define a restriction therebetween. 
     
     
       19. The valve of  claim 15 , wherein the heat source is configured to heat at least a portion of the downstream channel to substantially prevent (TRS) that enters the downstream channel from obstructing the channel. 
     
     
       20. The microfluidic system of  claim 15 , wherein the heat source comprising a heating element is disposed at a second surface of the first substrate, the second surface of the first substrate being opposite the first surface of the first substrate. 
     
     
       21. A microfluidic system, comprising: 
       a first substrate having a first planar surface and a second substrate having a first planar surface, the first planar surface of the first substrate bonded with the first planar surface of the second substrate, whereby the first and second substrates define, therebetween, a processing chamber, a source channel, and a downstream channel, the source channel joining the processing chamber at a first point and the downstream channel joining the processing chamber at a second point;  
       a thermally responsive substance (TRS) disposed to obstruct a passage between the processing chamber and downstream channel; and  
       a heat source in thermal contact with the TRS, wherein, upon actuation of the heat source, at least a portion of the TRS enters the downstream channel, thereby opening the passage.  
     
     
       22. A valve for use in a microfluidic system, comprising: 
       a thermally responsive substance (TRS) disposed to substantially obstruct the passage, wherein a length of the TRS obstructing the passage is greater than a width of the upstream channel adjacent the passage; and  
       a heat source in thermal contact with the TRS, wherein, upon actuation of the heat source, at least a portion of the TRS obstructing the passage moves out of the passage, thereby opening the passage.  
     
     
       23. The valve of  claim 22 , further comprising a reservoir of TRS adjacent the passage, wherein a width of the reservoir is greater than the width of the upstream channel. 
     
     
       24. The valve of  claim 23 , wherein the opening motion comprises a retraction of the TRS into the reservoir. 
     
     
       25. The valve of  claim 22 , wherein the passage comprises a surface and pressure present in the upstream channel urges at least a portion of the TRS against the surface. 
     
     
       26. The valve of  claim 22 , wherein at least 50% of the TRS moves out of the passage thereby opening the passage. 
     
     
       27. A valve for use in a microfluidic system, comprising: 
       a substrate defining a first and second channel joined by a passage, the first channel and the passage defining an opening therebetween;  
       a thermally responsive substance (TRS) disposed to substantially obstruct the passage, wherein a height of the opening is less than a height of the first channel adjacent the opening such that capillary action draws TRS into the passage and a surface tension of the TRS substantially prevents the TRS from entering the first or second channel; and  
       a heat source in thermal contact with the TRS, wherein, upon actuation of the heat source, an opening motion of the TRS opens the passage.  
     
     
       28. The valve of  claim 27 , wherein the second channel and the passage define an second opening therebetween, and further wherein a height of the second opening is less than a height of the second channel adjacent the passage. 
     
     
       29. The valve of  claim 28 , wherein the heights of each of the first and second openings are at least about 50% less than the corresponding heights of the first and second channels, respectively. 
     
     
       30. The valve of  claim 27 , further comprising: 
       a reservoir adjacent the passage, a height of the reservoir at a first location being less than a height of the reservoir at a second location, the first location being closer to the passage than the second location.  
     
     
       31. The valve of  claim 30 , wherein the reservoir comprises an a port for introducing TRS to the reservoir. 
     
     
       32. A microfluidic system, comprising: 
       a first planar substrate and a second, different planar substrate, a first surface of the first substrate and a first surface of the second substrate defining, therebetween, at least an upstream channel and a downstream channel joined by a passage, the passage comprising a first surface; and  
       a thermally responsive substance (TRS), at least a first portion of the TRS disposed, when the passage is in the closed state, to substantially obstruct the passage, wherein pressure present in the upstream channel urges at least a portion of the first portion of the TRS against the first surface of the passage.  
     
     
       33. A method for producing a valve for a microfluidic system, the valve being produced in the closed state, comprising: 
       providing a substrate defining a passage that joins an upstream and a downstream channel of the microfluidic system; and  
       introducing a mass of temperature responsive material (TRS) into a reservoir channel adjacent the passage;  
       heating at least the reservoir channel and passage, wherein capillary action draws at least a portion of the TRS into the passage thereby obstructing the passage.  
     
     
       34. A method for producing a valve for a microfluidic system, the valve being produced in the closed state, comprising: 
       providing a substrate defining (1) a passage that joins an upstream and a downstream channel of the microfluidic system and (2) a reservoir joining the passage, wherein a height of the reservoir at a first location is less than a height of the reservoir at a second location, the first location of the reservoir being closer to the passage than the second location;  
       heating at least the reservoir and passage;  
       introducing a mass of temperature responsive material (TRS) into the reservoir at least until a portion of the TRS reaches the first location of the reservoir, wherein capillary action draws TRS into the passage thereby obstructing the passage.